Technical Field
The present invention relates to an organic EL lighting device having an organic electroluminescent element (hereinafter, abbreviated as the organic EL element) as a light emission source.
Description of the Related Art
The commercialization of the organic EL lighting device as a planar light source, which is a thin film and can achieve light emission with high luminance by driving at a low voltage, is progressing.
When the light-emitting surface of the organic EL lighting is intended to be increased in area, the resistance value of a transparent electrode of ITO or the like which is generally used in the organic EL element is limited to be about 1.0×10−4 Ω·cm, and it cannot be said that this value is sufficiently low. For this reason, when the distance between the transparent electrode and a power supply unit increases, an electric current is not sufficiently supplied thereto due to wiring resistance, and thus a problem arises in which luminance unevenness occurs.
In this regard, in order to decrease the resistance value of the transparent electrode, an auxiliary electrode or an auxiliary wiring made of a lower resistance material is provided on the transparent electrode or in the transparent electrode. In general, such an auxiliary electrode or an auxiliary wiring is formed by a metal, an alloy, or a stacked structure thereof (see JP 2012-69450 A and JP 2012-22878 A). For example, an electrode pattern of a stacked structure such as MAM (molybdenum-aluminum-molybdenum) is formed by photolithography.
Furthermore, an auxiliary electrode or the like is also attempted to be formed by a printing method, and, for example, WO 2005/041217 A describes that an auxiliary electrode is formed on a transparent electrode by screen printing and an organic layer such as an organic EL light-emitting layer is stacked on the auxiliary electrode.
However, in the organic EL element manufactured as described above, when the formation of the coating film of the organic layer including the light-emitting layer on the auxiliary electrode, particularly, on the edge portion of the pattern, is not sufficient, short occurs between negative electrodes to be formed on the organic layer so that the electric current is concentrated on this portion, and thus a problem arises in which light emission may not be achieved in some cases.
For this reason, attempts have been made in which a problematic portion is covered with an insulating coating film. However, since the auxiliary electrode or the like as described above blocks light from the light-emitting layer, light emission from the transparent electrode substrate surface is not entire surface light emission, and the light emission looks like a black (non-light-emitting) stripe shape or mesh shape corresponding to the shape of the pattern of the auxiliary wiring or the shape of the insulating pattern.
Therefore, from the viewpoint of enhancing the light extraction efficiency, there is also a demand that the entire surface of the light-emitting surface emits uniformly light when the auxiliary electrode or the like is provided in order to obtain surface light emission at a large area.